基于光纤光栅传感技术的静压沉桩贯入特性及影响因素研究

Study of penetration characteristics and influence factor of jacked pile based on fiber bragg grating sensing technology

针对黏性土中静压沉桩贯入特性方面的研究相对较少的状况,基于光纤光栅(fiber bragg grating,简称FBG)传感技术,考虑开口、闭口不同桩端形式和不同桩径,研究了静压沉桩过程中沉桩阻力、桩身轴力以及桩身单位侧摩阻力的变化规律。通过静压沉桩模型试验,分析了桩端形式、桩径、沉桩深度等因素对沉桩阻力、桩身轴力及桩身单位侧摩阻力的影响规律。研究结果表明:FBG传感技术对黏性土中静压沉桩阻力的测试性能优越,能够准确体现静压管桩的贯入特性。沉桩结束时开口和闭口试桩的桩端阻力分别约占沉桩阻力的66.7%、59.5%。沉桩过程不可忽略开口土塞效应和桩径对沉桩阻力的影响。桩身轴力的分布形式不会因桩端形式而发生改变。桩径140 mm试桩的桩身轴力传递性能优于桩径100 mm试桩,两试桩桩身轴力递减率分别为40.8%、34.2%。开口试桩内管和外管桩身单位侧摩阻力最大值分别为1.67、4.83 kPa,均小于闭口试桩。贯入深度为90 cm时桩身单位侧摩阻力最大值随着桩径增加而增大,同一深度桩径越大桩身单位侧摩阻力"侧阻退化"越明显。入土深度为30 cm时两不同桩径桩身单位侧摩阻力减幅相差0.93 kPa。确定静压贯入沉桩阻力时考虑基于黏性土的侧阻退化后实际值更为合理。

The researches on sinking characteristics of jacked pile in clayey soil are relatively few. In this study, variations of pile sinking resistance, axial force and unit skin friction during jacked pile sinking were studied based on fiber Bragg grating sensing technology, considering the different pile end forms(such as open-ended and close-ended pile) and different pile diameters. Jacked pile sinking model tests were performed to determine the influences of pile ending form, pile diameter and pile sinking depth on pile sinking resistance, axial force and unit skin friction. The results shows that the requirement of FBG technology shows superior performance in testing sinking resistance of jacked piles in clayey soil, which can accurately reflect the penetration characteristics of jacked piles. The end resistance of open-ended and close-ended piles accounts for 66.7% and 59.5% of the piling resistance, respectively when sinking pile ends. The effects of open soil plug effect and pile diameter on pile sinking resistance can not be neglected. The distribution of the axial force of the pile shaft is not changed due to the pile end forms. The axial force transmission performance of pile with a diameter of 140 mm is better than that with 100 mm pile diameter. The decline rate of the axial force of the two piles is 40.8% and 34.2%, respectively. The maximum unit skin friction of the inner and outer tube piles of the open-ended pile is 1.67 kPa and 4.83 kPa, respectively, which are smaller than that of the close-ended pile. When the sinking depth is 90 cm, the maximum unit skin friction of the pile increases with increasing the pile diameter, and the larger pile diameter at the same depth results in more obvious degradation of the unit skin friction of the pile.